As Benjamin Franklin once wrote, “In this world nothing can be said to be certain, except death and taxes.” Although some of us are clearly better than others at dodging the ­in­evitable, in the end Mother Nature at least will always win. But along the path of life, people vary greatly in how often they get injured, incur illness or coast along in a comfortable state of health.

Considered at a distance, genetics and luck seem to explain a lot. But if we really understood why some people live longer than others, we would likely have diminished the gap by now. When epidemiologists and physicians discover some lifestyle choice or biological factor that leads to a longer and healthier life, they can then attempt to design intervention programs to ameliorate the health prospects of the population as a whole.